1. Field of the Invention
The present invention relates to a fly back transformer (to be called "FBT" below) which generates a high voltage to be supplied to a cathode ray tube of a TV or a monitor. Particularly, the present invention relates to a focus unit of an FBT, which is installed on a side of the FBT, for adjusting the focus and screen voltages of a cathode ray tube. More specifically, the present invention relates to a focus unit of an FBT, in which a slider spring for adjusting the focus volume can be easily installed on a volume bar, and the focus and screen voltages can be controlled in a sure manner. That is, focus and screen voltage adjusting round resistor patterns are formed on volume boards of the focus unit respectively, a supporting shaft is inserted into a central through hole of the round resistor pattern, a connecting pin is inserted into the supporting shaft, a pair of cables are inserted into a volume case so as for the cables to be connected to the lower ends of the connecting pins respectively, a pair of actuation knobs are inserted into a cover, a slider spring is installed within each of volume bars, and the lower end of the slider spring is movably connected to the round resistor pattern.
2. Description of the Prior Art
In the generally known conventional FBT, high and low voltage bobbins which are installed within the FBT case generate a high voltage to supply it through an anode cable to a cathode ray tube of TV or monitor. Here, the focus unit which is installed on a side of the FBT case varies the focus and screen voltages.
FIG. 1 illustrates the conventional focus unit of the FBT. Referring to FIG. 1, a focus volume knob 53 is integrally formed with a rotating piece 54 which extends into a main body 52 of a focus unit 51. Upon the rotating piece 54, there is installed a slider 55 having two contacts. There is installed a board 58 on which a resistor pattern 57 having a variable contact point 57a and a central contact point 57b is printed. On the board 58, there is installed an output pin 59 for being coupled with the board 58, and the inside of the main body 52 is coated with an insulating resin 60.
In this conventional focus unit 51 constituted as described above, in order to step up or down the focus and screen voltages, if the focus volume knob 53 (extending to the outside of the main body 52) is manually turned, the slider 55 together with the rotating piece 54 is rotated, so that the voltages can be stepped up or down along the resistor patterns 57. Under this condition, the slider 55 has two contact points 56 and 56', and one (56) of the contact points is connected to the variable contact point 57a of the circuit pattern 57 to step up or down the focus or screen voltage, while the other (56') of them is connected to the central contact point 57b for outputting an output through a resistor.
However, in the conventional focus unit as described above, in order to vary the focus and screen voltages as shown in FIG. 2, the slider 55 having the two contacts 56 and 56' is installed on the end of the adjusting knob 53. In this state, the variable contact point and the central contact point 57a and 57b are printed on the circuit pattern 57, with the result that the structure is complicated, and defects are caused in the contact points.
Further, as shown in FIG. 1, the height between the two contact points 56 and 56' are very small since they are formed on a flat spring, and therefore, defects occur in drawing the focus and screen voltages due to the limitation of the elasticity. Further, during the adjustment of the volume, the arc is transmitted to the slider, with the aggravation of the electrical characteristics of the slider.